This invention relates to using the kinetic energy of water impounded behind a dam to compress air, which is then stored for later generation of power.
Of the total number of dams in existence today only a small percentage have the capability to generate electric power, with the remainder being used primarily for flood control. In many of these dams the volume flow rate of the river they impound is not normally considered large enough to make continuous power generation economically practical even though over an entire day a large amount of energy passes over the spillway. However, since the stream flow downstream of these dams must remain constant, it is not possible to store the total kinetic energy capacity of each day's stream flow for use to produce a significant level of energy during the period of peak power demand.
A related problem arises on the larger dams from which hydroelectric power is already produced in the conventional manner. Again, since stream flow must be kept relatively constant, at times of reduced power demands excess water must be passed through the dam without the generation of power. Heretofore two solutions have been utilized to alleviate this problem. In the first all the water required to maintain stream flow is used to generate power at all times. The excess power generated during periods of low demand is then used to pump water from the reservoir behind the dam, thus temporarily lowering the reservoir, to a storage area which is separated from the dam. Then during periods of high power demand the stored water is allowed to flow back to the dam refilling the reservoir. While pump storage does permit maximum utilization of the flow generated by the impounded river, it is only possible with dams which are sited in an area where a large storage area can be obtained above the level of the dam. In addition, there are severe efficiency losses associated with the transfer of the water from the reservoir behind the dam to the storage area and then back to the reservoir.
A second method of utilizing the entire stream flow is to construct a secondary dam downstream of the hydroelectric dam. Then during peak power periods the normal stream flow can be exceeded to produce this power and the surplus water can be stored behind the secondary dam for release when power demand necessitates less than the normal amount of flow be used for power generation. However, the cost of constructing a secondary dam is considerable and it can be done only where the physical makeup of the river permits.
Accordingly, only in a few of the many hydroelectric dams presently in existence is it economically feasible to utilize the entire stream flow to generate power on a full-time basis. On all of the other dams, a portion of the stream flow must be bypassed around the dam with a resulting loss of power generation capacity.
Furthermore in all hydroelectric dams of the prior art, water is dropped through a penstock over a considerable portion of the head created by the dam in order to obtain the necessary velocity to drive the turbines which are used to generate power. Accordingly, the water becomes quite agitated and in the process absorbs nitrogen which is harmful to fish downstream of the dam. Also even though protective measures are taken, a large number of fish are drawn along with the flow of water through the turbines and are beat to death by the turbine blades. In addition, the very nature of water as a working fluid to drive turbines necessitates very low speed turbine operation which is inimical to high turbine efficiency.
In addition to the above problems, since the flow of a river behind a hydroelectric dam of the present type is in a high state of flux, there is a large amount of turbidity, whereby silt is build up behind the dam over a period of time. On the other hand, if normal stream flow could be allowed continuously to exist, even though electric power is not being generated, this phenomenon would not occur as the silt would continue to pass downstream with the river flow.